Chapter 14 - Hydrogels and hydrogel composites for 3D and 4D printing applications

Abstract

Hydrogels have found widespread use in tissue engineering and functional devices because of their biomimetic properties and multifunctionalities. As a promising fabrication technique, three-dimensional (3D) printing is able to construct hydrogels into complex artificial tissues and soft robotics with precise control. In this chapter, we first provide a brief introduction of 3D printing methods and general principles that make a hydrogel useful for 3D printing. Subsequently, we discuss the relationships of structure and property of hydrogels (based on natural polymers and synthetic polymers) and hydrogel composites (double network hydrogels, particle-reinforced hydrogels, and fiber-reinforced hydrogels), the control of key factors (viscosity, shear thinning, thixotropy, and interfacial bonding) in 3D printing, and its effect on printability of hydrogels and fidelity of constructs. Additionally, we also present the applications of 3D printed hydrogels as well as recent progress of hydrogel and hydrogel composites in 4D printing applications. Finally, challenges and future perspectives on 3D/4D printing of hydrogels will be discussed.